Suction dredges normally have a downwardly and forwardly inclined ladder carrying a suction pipe which has a suction mouth at its forward end and a rotatable cutter head just forward of such mouth. The head normally is driven by a shaft extending along the ladder from a motor on the upper end of the shaft. Usually the cutter head has a plurality of angularly spaced, toothed ribs spiralling divergently rearwardly from a hub at the forward end of the drive shaft. When sand or muck is being dredged, no problems normally arise. When the cutter head is working in hard lumpy clay, sandstone, coral, or other fossil or rock formations, however, problems are encountered in the production of large hard lumps that pass through the cutter head and are large enough to clog or damage the suction and discharge lines and the dredge pump. Clogging or stopping of the lines necessitates time-consuming down-time clean-out operations. Pump damage necessitates expensive down-time replacement or repair.
The foregoing problems were solved by the invention disclosed in my aforesaid copending patent application by the provision of an open-work rotatable crusher journalled on the cutter head drive shaft and driven by a gear train between the cutter head and the crusher. Such a solution, however, while most effective, is somewhat complicated and expensive because the crusher is mounted for rotation and requires a gear drive.